1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to image scanning, and in particular, to removing or reducing show-through in a medium during scanning performed with an image scanner.
2. Description of the Related Art
Image scanners (hereinafter called “scanners”) optically scan a medium such as a document, a drawing, a photograph, or a film, detect the intensity of light reflected from or transmitted through the medium to obtain image information, and then, process the image information in various ways.
CMOS image sensor (CIS) and charge-coupled device (CCD) are generally used in various scanner applications.
FIG. 1 illustrates the optical structure of a related art CIS type scanner. Referring to FIG. 1, red (R), green (G), and blue (B) beams are sequentially emitted by RGB LEDs onto a medium placed on a glass platen and the light which is reflected from the medium placed on the glass platen is detected by a photo transistor.
FIG. 2 illustrates the optical structure of a related art CCD type scanner.
Referring to FIG. 2, light that is emitted by a lamp and passes through an aperture is then reflected from mirrors and detected by a CCD linear array.
The related art CIS and CCD image sensors are widely used in the art as scanners or multi-function printers.
In the exemplary embodiments described below, the term scanners include but is not limited to multi-function printers and all other devices that can operate according to the previously described mechanisms.
FIGS. 3A and 3B illustrate exemplary embodiments which show-through is present within an image scanned by related art scanning devices.
Referring to FIGS. 3A and 3B, due to the thinness and high light permeability of a medium such as a newspaper or a printing paper, a scanner detects desired information from a front side of the medium and also undesired information from a back side of the medium. This phenomenon is known as show-through. Thus, various techniques have been proposed to remove show-through by a scanner.
For example, U.S. Pat. No. 6,067,170 entitled “Image forming apparatus for indicating completion of scanning for both sides of an original document” (See FIGS. 4 and 5) and Korean Laid-open Patent Application No. 1997-0071165 entitled “A copy paper scanning apparatus and image forming apparatus employing the same” have presented a technique for removing undesired information sensed from a back side of a medium by separately scanning both front and back sides of the medium with an Automatic Document Feeder (ADF) and comparing data scanned from both front and back sides of the medium with each other. That is, show-through information is removed from the back side of the medium by using multiple image input sensors to scan both the front and back sides of the medium in one-pass or by using a turn-over unit.
Another approach for removing show-through has been proposed in “A multiscale approach to restoring scanned color document images with show-through effects” Document Analysis and Recognition, 2003. Proceedings, Seventh International Conference on 3-6 Aug. 2003 page 584-588 vol. 1. The multiscale approach includes scanning a front side of the medium with show-through, analyzing the front side image, and estimating and removing show-through information from the front side image.
However, the above-described approaches require use of an expensive ADF and a plurality of sensors, thus increasing manufacturing costs, design complexity, and failure rate. Furthermore, the multiscale approach that involves scanning the front side image, and estimating and removing show-through information cannot completely eliminate show-through.